HAL Id: hal-00664520
https://hal.archives-ouvertes.fr/hal-00664520
Submitted on 30 Jan 2012HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Novel in situ electrochemical deposition of platinum
nanoparticles by sinusoïdal voltages on conducting
polymer films.
Stelian Lupun, Boris Lakard, Jean-Yves Hihn, Jérôme Dejeu
To cite this version:
Stelian Lupun, Boris Lakard, Jean-Yves Hihn, Jérôme Dejeu. Novel in situ electrochemical deposition of platinum nanoparticles by sinusoïdal voltages on conducting polymer films.. Synthetic Metals, Elsevier, 2012, 162 (1-2), pp.193-198. �hal-00664520�
Novel in situ electrochemical deposition of platinum nanoparticles by sinusoidal voltages on conducting polymer films
Stelian Lupua, , Boris Lakardb, Jean-Yves Hihnb, Jérôme Dejeuc
a
Department of Analytical Chemistry and Instrumental Analysis, Faculty of Applied Chemistry and Materials Science, University Politehnica of Bucharest, Polizu Street 1-5, 011061 Bucharest, Romania
b
Institut UTINAM, CNRS-UMR 6213, Université de Franche-Comté, 16 route de Gray, Besançon Cedex 25030, France
c
Institut FEMTO-ST, CNRS-UFC-ENSMM-UTBM, AS2M Department, 24 rue Alain Savary, 25000 Besançon, France
Abstract
Platinum (Pt) nanoparticles were successfully electrodeposited in situ on an organic
conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), using for the first
time sinusoidal voltages of various frequencies in a chloroplatinic acid solution. The
organic PEDOT matrix was electrodeposited on Pt electrode chips. The Pt electrode
chips consist of a 150 nm Pt layer deposited on 100-oriented standard 3’’ silicon wafers.
The cyclic voltammograms of the PEDOT-Pt-nanoparticles composite material recorded
in 0.5 M H2SO4 aqueous solution demonstrated that Pt nanoparticles are
electrochemically active. Values of the roughness of the composite materials, measured
by optical non-contact 3D profilometry, ranging from 880 nm to 1.6 m were obtained
Corresponding author. Phone: +40 21 4023886; fax: +40 21 3111796 , E-mail address: *Manuscript
depending on the time of deposition of the nanoparticles. The PEDOT-Pt-nanoparticles
composite deposited by a sinusoidal voltage with a frequency range of 0.1 Hz – 100
kHz, 50 frequencies, has the largest active surface area (5.16 cm2) compared with other
composite coatings prepared in this work and those previously reported. Atomic force
microscopic (AFM) images revealed the presence of numerous deposited Pt
nanoparticles on the organic PEDOT polymer film.
Keywords: Atomic force microscopy, Sinusoidal voltage,
Poly(3,4-ethylenedioxythiophene), Platinum metal nanoparticles
1. Introduction
The preparation of nanoparticles based composite materials has attracted
considerable interest due to their applications in electrochemical sensors and biosensors
[1-6]. Noble metal nanoparticles (NP) have been incorporated in conducting polymers
(CPs) using various preparation procedures [7-10]. Usually the NPs are prepared via a
chemical route [11-13] and are then incorporated into CP layers by electrochemical
polymerization of the appropriate monomer [7] or using the layer-by-layer deposition
technique [14, 15]. Recently, a great deal of interest has been devoted to innovative
synthesis route of Pt nanoparticles, for example by the help of ultrasound [16]. Another
possibility might lie in the in situ preparation of Pt nanoparticles achieved via
electrochemical methods [17-26]. In situ preparation of Pt nanoparticles has been
achieved via electrochemical methods, and in particular potentiostatic deposition at a
fixed potential value which is sufficiently negative to assure reduction of the appropriate
carried out in strong acidic solutions by applying a constant potential for a fixed period
of time or by potential cycling in appropriate potential ranges.
The aim of this paper is to demonstrate the suitability of a new in situ
electrodeposition preparation procedure based on electrochemical impedance
spectroscopy (EIS) technique for Pt nanoparticles deposition on PEDOT coatings. To
this purpose, in situ electrochemical preparation of Pt nanoparticles on PEDOT films
using sinusoidal voltages of various frequencies is reported here. Use of sinusoidal
signals for in situ preparation of Pt nanoparticles is first reported here and is in fact an
innovative aspect of this paper in the field of in situ nanoparticles electrodeposition. It is
worth to note that the proposed approach is similar to the EIS technique, which makes
use of the same materials and method. The use of large amplitude sinusoidal voltages
eliminated the possible reduction of proton during the Pt nanoparticles deposition and
this resulted in a finer control of the nanoparticles size and roughness of the composite
coatings. The resulting composite modified electrodes were investigated in 0.5 M
H2SO4 aqueous solution by cyclic voltammetry (CV), which revealed that Pt
nanoparticles are electrochemically active. The PEDOT-Pt-nanoparticles composite
coatings were further characterized by the AFM technique.
2. Experimental
2.1. Chemicals
All chemicals were used as received without further purification.
3,4-ethylenedioxythiophene (EDOT, Aldrich) was used for electrochemical preparation of
aqueous solutions. Freshly prepared solutions were used for electrochemical
measurements.
2.2. Electrochemical measurements
The electrochemical experiments were carried out with an Autolab
potentiostat/galvanostat 30 (Ecochemie, The Netherlands). A conventional
three-electrode system was used, including a Pt three-electrode chip as the working three-electrode, a
platinum wire as the auxiliary electrode, and a saturated calomel electrode (SCE) as the
reference electrode. All electrochemical measurements were carried out at room
temperature, under a high purity nitrogen atmosphere. The platinum electrode chips
(0.64 cm2) were fabricated according to a procedure previously reported [27]. Before
each electrochemical measurement, the surface of the working electrode was checked
by cyclic voltammetry in aqueous solution containing 1 mM K3Fe(CN)6 and 0.1 M KCl.
The impedance spectra were recorded through FRA2 soft of the Autolab potentiostat in
the frequency range 0.1 Hz – 100 kHz using a sinusoidal excitation signal (single sine)
with excitation amplitude (Eac) of 50 mV. A variety of frequency domains ranging
from 100 kHz to 0.1 Hz were used for in situ preparation of Pt nanoparticles.
2.3. Surface analysis of PEDOT-Pt-nanoparticles composite coatings
Polymer morphology examinations were performed using a commercial Atomic Force
Microscope (stand-alone SMENA scanning probe microscope NT-MDT, Russia) in the
contact mode. The experiments were conducted in a controlled environment with a
laminar flow (humidity 30 % and 25°C). Adhesion of the polymer films was estimated
0.3 N/m, was fixed, and the substrate moved vertically. Pull-off measurements were
taken with a cantilever to which a borosilicate sphere (r = 5 µm radius) was glued on the
free extremity and beneath it (Novascan Technologies, Ames, USA). Consequently,
pull-off force represents in this case the adhesion between the borosilicate sphere on the
tip AFM cantilever and the substrate. Ten measurements were taken at different points
on the same sample with a driving speed of 1 µm/s. Roughness of the polymer films
was also determined by AFM.
2.4. In situ electrodeposition of Pt nanoparticles on PEDOT
The composite PEDOT-Pt-nanoparticles films were prepared by a two-step method.
Firstly, the PEDOT layer was electrodeposited from an aqueous solution containing
0.01 M EDOT, and 0.1 M LiClO4 as a supporting electrolyte by potential cycling in the
potential range from open-circuit potential, OCP, to +1.0 V / SCE and reversed back to
-0.6 V / SCE, at a scan rate of 0.05 V s-1 for 5 or 10 consecutive scans, respectively. In
the second step, in situ deposition of Pt nanoparticles was carried out in 0.001 M
K2PtCl6, 0.1 M HClO4 aqueous solution by applying the following procedure:
sinusoidal voltages of various frequency ranges, i.e. 100 kHz – 0.1 Hz, 100 – 10 kHz,
with an excitation amplitude (Eac) of 50 mV were applied at a fixed dc potential value
of -0.20 V / SCE. The resulting composite modified electrode is referred to as
Pt/PEDOT-Pt-nanoparticles.
3. Results and discussion
Figures 1A and 1B show the CVs recorded during electrochemical deposition of
PEDOT coating performed on a naked electrode. Polymerization of the EDOT
monomer takes place in the potential range from 0.85 to 1.00 V / SCE, as can be seen
from the increase in anodic current. Growth of the organic PEDOT layer was controlled
by the potential cycle number applied in the electrochemical polymerization process,
namely 5 (see Fig. 1A) or 10 (see Fig. 1B) consecutive scans.
Figure 1 near here
3.2. Optimisation of the PEDOT-Pt-nanoparticles composite coatings preparation procedure
The potentiostatic deposition of Pt nanoparticles onto PEDOT films is usually
performed in strong acidic solutions, at negative potential values, i.e. -0.2 to -0.3 V. Due
to high proton concentration it may be possible that at such negative potential values
required for the reduction of platinum precursors to metallic states, the proton reduction
can occur simultaneously with the Pt nanoparticles deposition. To this purpose, we
investigated the electrochemical behaviour of naked Pt electrode chips in 0.1 M HClO4
aqueous solution. Figure 2A reports the cyclic voltammograms recorded at Pt electrode
in acidic solution. From this figure one can observe that the proton reduction starts at a
potential value of ca. -0.3 V / SCE. Furthermore, the Pt/PEDOT modified electrode was
also investigated by cyclic voltammetry in 0.1 M HClO4 aqueous solution. From Fig.
2B it can be seen that there is no proton reduction until a potential value of -0.3 V /
SCE. Therefore, the deposition potential value used for the in situ electrodeposition of
Pt electrode, the modified electrode was immersed in chloroplatinic acid solution and
the preparation procedure, described in Section 2.4, was applied for in situ Pt
nanoparticles electrodeposition on PEDOT films.
Figure 2 near here
3.3. Preparation of PEDOT-Pt-nanoparticles composite coatings by sinusoidal voltages Various sinusoidal voltages were applied for in situ deposition of Pt nanoparticles on
PEDOT layer. The duration of the measurements depends on the frequency range used,
which resulted in different Pt nanoparticles sizes, that is from 120 s up to 480 s.
Moreover, the amplitude (Eac) of 50 mV of the sinusoidal excitation signal (single
sine) was chosen to allow for the fact that this large amplitude can contribute to fine
control of nanoparticles size. Figure 3A reports the impedance spectrum recorded at the
Pt/PEDOT modified electrode in chloroplatinic acid solution in the frequency range 100
kHz – 0.1 Hz. Appearance of a capacitive loop can be observed in the high frequency
range of 100 – 18 kHz. This loop is magnified in the inset of Fig. 3A, and should be
attributed to the interfacial behaviour between the Pt/PEDOT modified electrode and
the solution. Two other loops can be observed in the medium frequency range of 18 kHz
– 3 kHz and 3 kHz – 100 Hz. These loops can be associated with Faradaic reactions. These reactions should be the reduction of the precursor Pt4+ complex ions to Pt2+, and
then to Pt0 with the formation of Pt nanoparticles. Finally, at low frequencies, the
impedance spectrum is dominated by the Warburg impedance. This impedance
spectrum is depicted as Bode plot in Fig. 3B. From the Bode plot one can observe that
theoretical value of -1, while for high frequencies a slope close to 3, indicative for diffusion-reaction reduced impedance, is obtained. Furthermore, the phase vs. log f plot
depicted in Fig. 3B shows that at low frequencies a phase of ca. 80 degrees is obtained,
while for high frequencies the phase tends to zero, which is indicative of capacitive
behaviour. A value of ca. 78 Ohms for the charge transfer resistance (Rct) can be
obtained from the Z’ vs. 1/2 plot, which is depicted in Fig. 3C. From this value, the exchange current density (i0) was determined as 1.29 x 10-4 A cm-2, according to the
equation (1): ) nFi ( / RT Rct 0 (1)
where n =4, and the other symbols have their usual significance [28].
Therefore, it is worth to note that the new preparation procedure allows for the
electrochemical parameters, such as charge transfer resistance and exchange current
density, to be also determined. This feature is brought by the EIS powerful technique
used in the Pt nanoparticles electrodeposition and can be considered as an advantageous
tool compared with the classical potentiostatic methods applied for nanoparticles
deposition.
Figure 3 near here
3.4. Electrochemical characterization of PEDOT-Pt-nanoparticles composite materials After deposition of Pt nanoparticles onto the PEDOT layer, the modified electrodes
were characterized in 0.5 M H2SO4 aqueous solution using cyclic voltammetry. Figure 4
reports the cyclic voltammograms recorded for various types of
range, the number of measured frequencies, and the number of deposition scans applied
in the preparation procedure of the PEDOT coatings. Two well-separated pairs of peaks
can be observed between -0.25 and 0.0 V / SCE, which are due to adsorption and
desorption of hydrogen atoms on Pt nanoparticles surfaces. Pt oxide formation occurred
in the potential range from 0.8 V to 1.0 V / SCE, and the corresponding reduction peak
of Pt oxide is located at 0.6 V / SCE. The features of the voltammograms were similar
to the polycrystalline Pt electrode, with typical peaks at -0.13 V and -0.05 V / SCE,
whereas the pure PEDOT the current is low and only influence by its capacitance. The
peak currents for the reduction waves located in the potential range -0.25 – 0.0 V / SCE
increased with deposition time corresponding to different frequency ranges and the
number of measured frequencies used in the preparation procedure.
It is important to notice the drastic increase in the anodic peaks, which rose from
2.6 µA at -0.05 V for naked Pt up to 126 A at -0.05 V /SCE, maximum met for nanoparticles deposited by a sinusoidal voltage (100 kHz-0.1 Hz, 50 frequencies, on
PEDOT deposited by 5 scans). These results demonstrate that Pt nanoparticles deposited
on PEDOT coating by a sinusoidal voltage were electrochemically active. By
comparison, nanoparticles prepared by classical potentiostatic methods, deposition time
1200 s [22], give electrodes with a similar behaviour.
The electrochemically active surface area can be estimated by using the
characteristic value of the charge density for a monolayer of hydrogen adsorbed on
polycrystalline platinum electrode, i.e. 0.21 mC cm-2 [23, 29-31]. The cyclic
voltammograms presented in Fig. 4 indicate that the PEDOT-Pt-nanoparticles
composite, deposited by a sinusoidal voltage with a frequency range of 0.1 Hz – 100
composite coatings prepared in this work and those previously reported [23]. The values
of the estimated electroactive surface area for the Pt nanoparticles composite coatings
are presented in Table 1.
Figure 4 near here
Table 1 near here
The thickness of the PEDOT layer influences the electrodeposition of Pt
nanoparticles as can be seen from Fig. 4 on the CV trace for a PEDOT coating obtained
by applying 10 consecutive deposition scans. In this case the increased thickness of the
PEDOT layer hindered the formation of Pt nanoparticles and as a result the hydrogen
adsorption-desorption peaks are not well defined. Therefore, an extended frequency
range and/or a larger number of measured frequencies should be used for the Pt
nanoparticles electrodeposition by sinusoidal voltages when thicker PEDOT coatings
are involved. The increased numbers of deposition scans used in the
electropolymerization of the EDOT monomer resulted in an enhanced surface area of
the electrode, as can be seen from Table 1, but the adsorption/desorption hydrogen
peaks are not well defined. Furthermore, the Pt electrode modified with a pure PEDOT
coating shows no peaks in the potential range from -0.25 to 0.0 V / SCE and this result
supports the above findings concerning the electrochemical activity of the Pt
nanoparticles.
2D and 3D AFM images were performed on PEDOT-LiClO4 films (Figures 5A and 5B)
and on PEDOT-Pt-nanoparticles composite films obtained by a sinusoidal voltage in
chloroplatinic acid solution at a fixed potential value of -0.20 V / SCE for the frequency
range 100 kHz – 0.1 Hz (Figures 6A and 6B). The AFM of the PEDOT-LiClO4 films
exhibited a granular, regular and homogeneous structure. Grain size is less than 200 nm
and height can be estimated at 80-90 nm.
Figure 5 near here
On the contrary, the PEDOT-Pt-nanoparticles films have a slightly different structure
since the surface showed a rougher relief, with a strong increase in heterogeneities. This
change of topography is due to the nanoparticles inserted in the polymer film. The
nanoparticles thus led to an increase in film roughness, and the height of the grains
growing on the nanoparticles can be estimated at 270 nm. Therefore, one can assume
that the nanoparticles size is approximately 170-180 nm.
Figure 6 near here
The adhesion force, known as the “pull-off force”, was measured for all polymer
coatings versus their electrodeposition conditions (with or without deposition of
nanoparticles). The pull-off values are presented in Table 2.
The results presented in this table show marked differences in the adhesion forces
between PEDOT-LiClO4 and Pt-nanoparticles samples. Indeed,
PEDOT-LiClO4 exhibited an attractive pull-off force of -40.4 nN. On the contrary, the pull-off
force was only included in the range between -5 and -15 nN, indicating a marked
modification in surface properties and proving once again the presence of Pt
nanoparticles. Moreover, the less negative pull-off values (- 3.79 and -5.13 nN) were
obtained with the thickest films (obtained through 50 frequencies instead of 5 or 10 for
the two other samples), confirming that the presence of Pt nanoparticles influences the
adhesion properties of the films.
3.6. Advantages of the novel reported preparation procedure
The presented results clearly show that the in situ electrodeposition of Pt nanoparticles
by using sinusoidal voltages offer some advantages compared with the potentiostatic
method. First of all, the novel procedure provides a finer control of the nanoparticles
size and especially of the surface roughness of the composite coatings. Values of the
roughness ranging from 880 nm to 1.6 m were obtained depending on the time of deposition of the nanoparticles Moreover, by applying a sinusoidal voltage over the dc
fixed voltage of -0.2 V / SCE in acidic media the proton reduction was totally hindered
thanks to the large amplitude of the sinusoidal voltage of 50 mV, even if it is shown that
under these experimental conditions the proton reduction starts at ca. -0.3 V / SCE (see
Fig. 2A). The large amplitude of the sinusoidal voltage used in this work prevented the
agglomeration of Pt nanoparticles and the proton reduction, resulting in a smaller size of
Pt nanoparticles and roughness values. The use of various frequencies pointed out that
employed, the peak currents were higher for the 0.1 Hz – 100 kHz range in comparison
with 10 – 100 kHz range, noting that the duration of the measurement was almost the
same. Furthermore, the peak currents of the adsorption / desorption of hydrogen are
comparable with those reported in Ref. 22, where the Pt nanoparticles were deposited
by potentiostatic method at -0.2 V in 1.1 mM H2PtCl6, 0.5 M H2SO4 solution for a
deposition time of 1200 s, which is 2.5 times higher in respect to the time used for the
Pt nanoparticles deposition by a sinusoidal voltage with a frequency range of 0.1 Hz –
100 kHz. Therefore, it can be concluded that the use of sinusoidal voltages in Pt
nanoparticles in situ electrodeposition provides a better control of the nanoparticles size
and surface roughness. Finally, it is worth to note that this new in situ preparation
procedure allows the estimation of the electrochemical parameters, such as charge
transfer resistance and exchange current density. This feature is brought by the EIS
powerful technique used in the Pt nanoparticles in situ electrodeposition and can be
considered as an appealing advantage compared with the classical potentiostatic
methods applied for metal nanoparticles deposition.
4. Conclusions
Pt nanoparticles were successfully electrodeposited in situ, for the first time, on PEDOT
organic conductive polymers using sinusoidal voltages of various frequencies in a
chloroplatinic acid solution. The cyclic voltammograms recorded in 0.5 M H2SO4
aqueous solution demonstrated that Pt nanoparticles deposited via this novel preparation
procedure are electrochemically active. Values of the roughness ranging from 880 nm to
novel in situ preparation procedure provides PEDOT-Pt-nanoparticles composite
electrode with a large active surface area (5.16 cm2) compared with other composite
coatings previously reported. The AFM measurements revealed the presence of
numerous deposited Pt nanoparticles on the organic PEDOT polymer film. The novel
reported method for Pt nanoparticles in situ electrodeposition on conducting polymer
films provides a better control of the nanoparticles size and surface roughness. This
work thus proposes a novel and efficient strategy for in situ electrochemical deposition
of Pt nanoparticles on an organic conductive polymer matrix.
Acknowledgements
S. Lupu greatly acknowledges the Invited Professor stage at the University of
Franche-Comté, France. Authors gratefully thank the MIMENTO platform of the FEMTO-ST
Institute in Besançon, France.
REFERENCES
[1] J. Wang, Anal. Chim. Acta 500 (2003) 247-257.
[2] X. Luo, A. Morrin, A.J. Killard, M.R. Smyth, Electroanalysis 18 (2006)
319-326.
[3] S. Guo, S. Dong, Trends Anal. Chem. 28 (2009) 96-109.
[4] M. Sastry, Pure Appl. Chem. 74 (2002) 1621-1630.
[5] C.M. Welch, R.G. Compton, Anal. Bioanal. Chem. 384 (2006) 601-619.
[6] F.W. Campbell, R.G. Compton, Anal. Bioanal. Chem. 396 (2010) 241-259.
[7] A. Nirmala Grace, K. Pandian, Electrochem. Commun. 8 (2006) 1340-1348.
[9] S. Senthil Kumar, J. Mathiyarasu, K. Lakshminarasimha Phani, J. Electroanal.
Chem. 578 (2005) 95-103.
[10] K.M. Manesh, P. Santhosh, A. Gopalan, K.P. Lee, Talanta 75 (2008)
1307-1314.
[11] K.E. Christodoulakis, D. Palioura, S.H. Anastasiadis, M. Vamvakaki, Top
Catal. 52 (2009) 394-411.
[12] Q.Y. Deng, B. Yang, J.F. Wang, C.G. Whiteley, X.N. Wang, Biotechnol. Lett.
31 (2009) 1505-1509.
[13] B. Qu, Y.-T. Xu, S. Lin, Y.-F. Zheng, L.-Z. Dai, Synth. Met. 160 (2010)
732-742.
[14] K. Karnicka, M. Chojak, K. Miecznikowski, M. Skunik, B. Baranowska, A.
Kolary, A. Piranska, B. Palys, L. Adamczyk, P.J. Kulesza, Bioelectrochemistry
66 (2005) 79-87.
[15] P.J. Kulesza, K. Karnicka, K. Miecznikowski, M. Chojak, A. Kolary, P.J.
Barczuk, G. Tsirlina, W. Czerwinski, Electrochim. Acta 50 (2005) 5155-5162.
[16] B.G. Pollet, Int. J. Hydrogen Energy 35 (2010) 11986-12004.
[17] Y. Liu, M. Yang, Z. Zheng, B. Zhang, Electrochim. Acta 51 (2005) 605-610.
[18] F. Maillard, E.R. Savinova, U. Stimming, J. Electroanal. Chem. 599 (2007)
221-232.
[19] C.W. Kuo, C. Sivakumar, T.-C. Wen, J. Power Sources 185 (2008) 807-814.
[20] S. Patra, N. Munichandraiah, Langmuir 25 (2009) 1732-1738.
[21] V. Zin, B.G. Pollet, M. Dabalà, Electrochim. Acta 54 (2009) 7201-7206.
[22] L.Y. Bian, Y.H. Wang, J.B. Zang, J.K. Yu, H. Huang, J. Electroanal. Chem.
[23] Y. Zhou, H. Xian, F. Li, S. Wu, Q. Lu, Y. Li, L. Wang, Electrochim. Acta 55
(2010) 5905-5910.
[24] C. Sivakumar, Electrochim. Acta 52 (2007) 4182-4190.
[25] T. Spataru, M. Marcu, A. Banu, E. Roman, N. Spataru, Electrochim. Acta 54
(2009) 3316-3319.
[26] D.-M Zeng, Y.-X Jiang, Z.-Y Zhou, Z.-F Su, S.-G Sun, Electrochim. Acta 55
(2010) 2065-2072.
[27] O. Segut, B. Lakard, G. Herlem, J.Y. Rauch, J.C. Jeannot, L. Robert, B. Fahys,
Anal. Chim. Acta 597 (2007) 313-321.
[28] A.J. Bard, L.R. Faulkner, Electrochemical Methods, Wiley, New York, 1980.
[29] S. Trasatti, O.A. Petrii, Pure Appl. Chem. 63 (1991) 711-734.
[30] K. Shimazu, D.Weisshaar, T. Kuwana, J. Electroanal. Chem. 223 (1987)
223-234.
Captions to figures
Fig. 1. Cyclic voltammograms recorded during electrochemical polymerization of
EDOT at the Pt electrode chip in an aqueous solution containing 0.01 M EDOT and 0.1
M LiClO4 as a supporting electrolyte. Potential scan rate: 0.05 V s-1. The first 5 (A) and
10 (B) consecutive scans are depicted, respectively.
Fig. 2. Cyclic voltammograms recorded at (A) Pt naked electrode chip and (B)
Pt/PEDOT modified electrode in 0.1 M HClO4 aqueous solution at a potential scan rate
of 0.05 V s-1.
Fig. 3. (A) Impedance spectrum recorded on Pt/PEDOT modified electrode at a fixed dc
potential value of -0.2 V for frequency range from 100 kHz to 0.1 Hz in an aqueous
solution containing 0.001 M K2PtCl6 and 0.1 M HClO4. (B) The Bode plot and (C) the
Z’, Z’’ vs. 1/2
plot of the impedance spectrum obtained as described in Fig. 3A.
Fig. 4. Cyclic voltammograms recorded at Pt/PEDOT-Pt-nanoparticles composite
modified electrodes and naked Pt electrode in 0.5 M H2SO4 aqueous solution at a scan
rate of 0.05 V s-1.
Fig. 5. (A) 2D and (B) 3D AFM images (contact mode) of PEDOT films obtained
Fig. 6. (A) 2D and (B) 3D AFM images (contact mode) of Pt-nanoparticles prepared in
situ on PEDOT film at a fixed potential value of -0.20 V for frequency range from 100
kHz to 0.1 Hz (5 deposition cycles for PEDOT matrix, 50 frequencies).
Table 1
The estimation of the electrochemically active surface areas of the polymer composite
modified electrodes.
Table 2
Estimation of the pull-off values, using AFM, of the polymer films in the presence or
Table 1. The estimation of the electrochemically active surface areas of the polymer
composite modified electrodes.
Composite electrode Electrochemically active surface area (cm2) PEDOT - LiClO4 (5 scans) -Pt nanoparticles deposited by a
sinusoidal voltage, ΔF = 100 kHz – 0.1 Hz, 50 frequencies 5.16
PEDOT - LiClO4 (5 scans) – Pt nanoparticles deposited by a
sinusoidal voltage, ΔF = 100 kHz – 10 kHz, 50 frequencies 4.64
PEDOT - LiClO4 (5 scans) – Pt nanoparticles deposited by a
sinusoidal voltage, ΔF = 100 kHz – 10 kHz, 10 frequencies 1.64
PEDOT - LiClO4 (10 scans) - Pt nanoparticles deposited by a
sinusoidal voltage, ΔF = 100 kHz – 10 kHz, 10 frequencies. 2.28 Table
Table 2. Estimation of the pull-off values, using AFM, of the polymer films in the presence or
absence of nanoparticles.
Sample Pull-off (nN)
PEDOT - LiClO4 5 scans - 40.4
PEDOT - LiClO4 (5 scans) -Pt nanoparticles deposited by a
sinusoidal voltage, ΔF = 100 kHz – 0.1 Hz, 50 frequencies - 5.13
PEDOT - LiClO4 (5 scans) – Pt nanoparticles deposited by a
sinusoidal voltage, ΔF = 100 kHz – 10 kHz, 50 frequencies - 3.79
PEDOT - LiClO4 (5 scans) – Pt nanoparticles deposited by a
sinusoidal voltage, ΔF = 100 kHz – 10 kHz, 10 frequencies - 9.45
PEDOT - LiClO4 (10 scans) - Pt nanoparticles deposited by a
sinusoidal voltage, ΔF = 100 kHz – 10 kHz, 10 frequencies. - 91.3
PEDOT-LiClO4 (10 scans) - Pt nanoparticles deposited by a
sinusoidal voltage, ΔF = 100 kHz – 10 kHz, 5 frequencies. - 14.2 Table
-100
0
100
200
300
400
-0.8
-0.4
0
0.4
0.8
1.2
E / V
j /
m
A cm
-2A
Figure 1A. Figure-1A-100
0
100
200
300
400
500
-0.8
-0.4
0
0.4
0.8
1.2
E / V
j /
m
A cm
-2B
Figure 1B. Figure-1B-120
-100
-80
-60
-40
-20
0
20
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
E / V
j /
m
A cm
-2A
Figure 2A. Figure-2A-80
-60
-40
-20
0
20
40
60
80
-0.4
-0.2
0
0.2
0.4
0.6
E / V
j /
m
A cm
-2B
Figure 2B. Figure-2B0
200
400
600
800
0
50
100
150
Z' (Ohm)
-Z''
(Ohm)
0 5 10 77 78 79 80 81 Z' / Ohm -Z '' / Oh mA
Figure 3A. Figure-3A0
0.5
1
1.5
2
2.5
3
-2
0
2
4
6
log f
log Z
0
20
40
60
80
100
ph
as
e / degree
s
log Z
phase
B
Figure 3B. Figure-3B0
40
80
120
160
0.0
0.5
1.0
1.5
2.0
2.5
3.0
1 /
w
2Z'
(Ohm)
0
200
400
600
800
- Z'' (Ohm)
Z'
Z''
C
Figure 3C. Figure-3C-2.00E-04
-1.50E-04
-1.00E-04
-5.00E-05
0.00E+00
5.00E-05
1.00E-04
1.50E-04
2.00E-04
-0.3 -0.1 0.1 0.3 0.5 0.7 0.9 1.1
Potential / V vs. SCE
Current / A
100 KHz-0.1 Hz; 50 frequencies; PEDOT-Pt-nano 5 scans 100-10 KHz; 50 frequencies; PEDOT-Pt-nano 5 scans 100-10 KHz; 10 frequencies; PEDOT-Pt-nano 5 scans 100-10 KHz; 10 frequencies; PEDOT-Pt-nano 10 scans Pt naked Figure 4. Figure-4Figure 5A. Figure-5A
Figure 5B. Figure-5B
Figure 6A. Figure-6A
Figure 6B. Figure-6B
